For quite some time Amazon was selling refurbished Kindle devices at a discount:
Now you can also get refurbished Kindle DX with 9.7″ screen and PDF support at $90.00 (18%) discount for $399.00.
It should be noted that refurbished Kindles come with the same 1 year warranty as new ones.
Thanks to reader UB for letting me know about this via a comment.
I’ll keep you updated on the stock status of all 3 models at it changes.